It is frequently desired for one purpose or another to detect, locate or monitor something in the ocean or on another body of water for example, it is frequently necessary to rescue people adrift in the ocean after a shipwreck or an airplane going down at sea. It is also frequently desired to measure currents or to monitor some other sea activity. Similarly, it is often necessary to locate or monitor objects on land; for example, air crashes at remote land locations are frequently at least as difficult to find as those in the ocean.
These various activities have been hampered by the fact that things adrift in a wide expanse of water are particularly hard to locate especially when active communication cannot proceed. Some of the steps which have been taken in the past toward location of people or objects at sea or on another body of water have included providing lights such as hand-held flashlights or beacons or oral radio communication so that the article at sea can be detected from a great distance. Special dyes have been employed to color the water and make a specific location more highly visible. For measuring currents over long distances, radio beacon communications to satellites are sometimes used, but it is not usual to avoid completely the effort to trace a floating object and simply to measure, for example, the salinity of the water and thus to trace a current back to a source. Measurements such as these, although not fully satisfactory, are in general use simply because on a hard, practical basis they represent the best there is.
One embodiment of present invention relates to an improved way of detecting, locating, monitoring or otherwise finding and keeping track of an object at sea or on another body of water. A floating object bearing a plurality of retroreflectors, sometimes known as corner reflectors, is placed in the water where it can be detected by the fact that it returns a beam of light or radiation at essentially 180.degree. reversal of path. Corner reflectors are known in the art, and taken alone, do not represent this invention. The floating object acts as a passive component in an entire system which can include means to send out a radiation signal to permit its detection by logic apparatus, so that the detection and location can, if desired, be automatic. For example a laser beam may be scanned across the surface of the water by suitable means and the reflective signal picked up and compared against the scanner signal which is being transmitted.
One of the advantages of the present system is that the reflected signal can be positively identified so as to eliminate interference or confusion resulting from random reflection of light from the ocean surface. It can detect and identify the specific components from a relatively great distance either at night or during the day, and needs no positive cooperation from people or apparatus at the sea location except for merely launching the reflector at the initiation of the need for detection. Even the initial launching can be automatic. For example, a plurality of the floating reflectors according to this invention can be releasably secured to the outer surface of an airplane on an overwater flight so that on landing at sea these floating reflectors are torn loose and thereupon float in the water to provide a basis of detection and sea rescue.
The reflector according to a preferred embodiment of the present invention comprises floating a head substantially lighter than water, with a ballast member secured thereto to cause the head to bob on the surface of the water in a predictable upright position. Positioned on the upper surface are a plurality of retroreflector elements arranged to provide reflection back to the source and covering a 360.degree. horizontal angle. The reflectors can cover the angle of the sky virtually or if need be, completely from horizon to horizon, so that a light signal received from any position above the surface of the water will be reflected back on itself, or, in one embodiment an angle of about 60.degree. from the vertical is covered. There is relative freedom of design to position the reflectors on the floating head so as to cover the entire sky or only a part of the sky, and one embodiment of the invention covers the sky area above an angle of about 30.degree. from the horizontal in cooperation with search means to detect the reflectors from a flying airplane which does not require detection from a point near the surface of the sea. In this embodiment of the invention, four reflectors are positioned on the upper device surface spaced 90.degree. from each other and inclined at an angle from the horizontal, such as about 30.degree.. The surfaces or facets in which the reflectors are mounted may be inclined at this angle, or the reflectors may be tipped or wedged at the desired angle. The retroreflector elements, and desirably also the surface or member, have hydrophobic surfaces either as a result of their composition or as a consequence of surface treatment or surface coating.
According to another embodiment of the invention the individual reflector units may be secured to or mounted on an object which is itself the subject of a search. For example, for detection of people lost at sea as a result of an airplane going down at sea, the reflector units may be secured to or mounted on a raft or other rescue device or on clothing or other articles worn by airplane occupants. For example, a pilot's helmet may have one or more reflector units mounted thereon.
Cooperating with the floating reflector of FIG. 1 or FIG. 3 is a base station which may be, and generally is, carried in an airplane to permit rapid covering of an extremely wide ocean area. According to a preferred embodiment, a laser beam generated in an airplane is reflected by a rapidly rotating mirror to scan the ocean. Such laser beam scanning equipment is known and is commericially available. Detection means also at the base station receives the reflected beam and analyzes it in a logic system. Desirably, the scanning rate is such that several scans of the beam pass across a floating reflector as an airplane flies across. When the signal-receiving means on the airplane records the reception of a pulsed signal of correct type and sequence, it is ascertainable that it is different from a random signal. As will be seen hereinafter, the system operates quite effectively from an airplane flying as high as 10,000 feet, weather permitting; greater altitude may be employed provided the equipment is adapted to operate with a weaker reflector signal. Ordinarily for sea rescue it may be preferred to operate from a position below 1,000 feet in order to take full advantage of a strong signal.
At the present time, it is intended that the system operate with relatively inexpensive continuous-wave lasers emitting in near infrared light ranges, but if desired, the system can operate with a visible, infrared or ultraviolet signal or other signal which can be reflected back on itself. Ordinary light sources rather than lasers may be used, but apparatus complications may more than cutweigh the savings in cost from the less expensive light source.
The system can be operated with a base station aboard ship or for some purposes with a land base station.